Simultaneous Stokes and anti-Stokes ultralow-frequency (ULF) Raman measurement down to ∼2 cm or 60 GHz is realized by a single-stage spectrometer in combination with volume-Bragg-grating-based notch filters. This system reveals its excellent performance by probing Brillouin signal of acoustic phonons in silicon, germanium, gallium arsenide, and gallium nitride. The deduced sound velocity and elastic constants are in good accordance with previous results determined by various methods. This system can shorten the integration time of the Brillouin signal with a good signal-to-noise ratio by more than 2000-fold compared to a Fabry-Perot interferometer (FPI). This study shows how a filter-based ULF Raman system can be used to reliably achieve Brillouin spectroscopy for condensed materials with high sensitivity and high signal-to-noise ratio, stimulating fast Brillouin spectrum measurements to probe acoustic phonons in semiconductors.
Despite some advances in the study of radiation injuries, effective methods of prevention and treatment of severe acute radiation syndrome or illness (ARS) are still lacking. Therefore, an in-depth understanding...
Divided aperture confocal microscopy (DACM) provides an improved imaging depth, imaging contrast, and working distance at the expense of spatial resolution. Here, we present a new method-divided aperture correlation-differential confocal microscopy (DACDCM) to improve the DACM resolution and the focusing capability, without changing the DACM configuration. DACDCM divides the DACM image spot into two round regions symmetrical about the optical axis. Then the light intensity signals received simultaneously from two round regions by a charge-coupled device (CCD) are processed by correlation manipulation and differential subtraction to improve the DACM spatial resolution and axial focusing capability, respectively. Theoretical analysis and preliminary experiments indicate that, for the excitation wavelength of λ = 632.8 nm, numerical aperture NA = 0.8, and normalized offset v = 3.2 of the two regions, the DACDCM resolution is improved by 32.5% and 43.1% in the x and z directions, simultaneously, compared with that of the DACM. The axial focusing resolution used for the sample surface profile imaging was also significantly improved to 2 nm.
Confocal Brillouin microscopy (CBM) is a novel and powerful technique for providing non-contact and direct readout of the micro-mechanical properties of a material, and thus used in a broad range of applications, including biological tissue detection, cell imaging, and material characterization in manufacturing. However, conventional CBMs have not enabled high precision mechanical mapping owing to the limited depth of focus and are subject to system drift during long-term measurements. In this paper, a divided-aperture confocal Brillouin microscopy (DCBM) is proposed to improve the axial focusing capability, stability, and extinction ratio of CBM. We exploit high-sensitivity divided-aperture confocal technology to achieve an unprecedented 100-fold enhancement in the axial focusing sensitivity of the existing CBMs, reaching 5 nm, and to enhance system stability. In addition, the dark-field setup improves the extinction ratio by 20 dB. To the best of our knowledge, our method achieves the first in situ topographic imaging and mechanical mapping of the sample and provides a new approach for Brillouin scattering applications in material characterization.
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